Within the context of climate change, extreme climate events have accurred frequently. Extreme climate events have more significant and stronger impact than average state on social-economic development and ecological environment evolution. The coastal area of China is a region with high ecological vulnerability and is extremely sensitive to global climate change. Extreme climate events such as typhoon, strom surge, heavy rain, heat waves and drought occur frequently in the coastal area of China, resulting in grave consequences in term of sea level rise, sea water intrusion, urban waterlogging, reduction of agricultural and sideline production and so on, affect the regional socio-economic sustainable development directly, which poses a huge challenge and a serious threat to the ecological and environment protection and people’s living conditions.
Vegetation cover plays an important role in the ecological service function over the coastal area of China. Recently, extreme climate events such as high temperature and heatwave, heavy precipitation and drought have had a certain degree of impact on vegetation cover over the coastal areas, which lead to the change of regional primary net productivity, soil and water conservation, atmospheric regulation, climate maintenance and stability of the entire ecosystem. Given this, conducting research on characteristics of historical changes and its persistence, spatial differences and consistency with climate average state of extreme climate events, and explore the impact of extreme climate events on vegetation cover further are important precequisite for assessing the impact change on the ecological environment and social environmental over the coastal areas, which contributes to promoting regional ecological and environmental protection and ecological costruction preserve, and providing strong support for the decision-making of sustainable development of economy and society.
Based on daily temperature and precipitation dataset of 156 weather station records from 1961 to 2014 in the coastal area of China, 27 extreme temperature and extreme precipitation indices were calculated, and then the extreme climate events’ characteristics on terms of change trend and its persistence, periodicity, abruptness and spatial pattern were investigated comprehensively and thoroughly using a set of mathematical and statistical methods including trend analysis, Morlet analysis, Mann-Kendall test, accumulative anomaly analysis, Pettitt test, principal component analysis and correlation analysis. Additionally, based on GIMMS NDVI3g data, the temporal trends and its persistence, abrupt characteristics and spatial distribution of NDVI in the coastal area of China from 1982 to 2014 were analyzed. Finally, the impact of extreme climate events on NDVI were explored in the coastal area of China by employing correlation analysis and de-seasonalization methods. The main conclusions of this paper are as follows:(1) Extreme temperature events characteristics
An upward trend in warm extremes and a downward trend in cold extremes as well as diurnal temperature range (DTR) were found, and the decadal trend rates of the night extremes were obviously higher than those of the day extremes in the coastal area of China and its sub-regions. Generally, a decrease was observed in the multi-year averages of the frost days (FD0), ice days (ID0) and diurnal temperature range (DTR), and an increase was observed in the mutil-year averages of the summer days (SU25), tropical nights (TR20), minimum value of daily maximum temperature (TNx), minimum value of daily minimum temperature (TNn) and growing season length (GSL) from north to south. However, a little variation was observed in the multi-year averages of the cool days (TX10p), cool nights (TN10p), warm days (TX90p), warm nights (TN90p), maximum value of daily maximum temperature (TXx), maximum value of daily minimum temperature (TNx), cold spell duration index (CSDI) and warm spell duration index (WSDI) between the sub-regions and the entire coastal area of China. Primary period of extreme temperature indices varied from 2- to 8-year in the sub-regions. The mutation time of extreme temperature indices occurred mainly in the 1980s and the 1990s in all sub-regions. Additionally, the cold extremes and minimum values of daily maximum (minimum) temperature mutated earlier than those of the warm extremes and maximum values of daily maximum (minimum) temperature. In the coming period, the change trends of the extreme warm and extreme cold indices will continue as the trends of the past, respectively. Extreme temperature warm (cold) indices both exhibited high contributions to the daily average and daily maximum (minimum) temperatures. DTR, TNx and so on showed a weak indicative to the daily average and daily maximum (minimum) temperatures.(2) Extreme precipitation events characteristics
Except consecutive moisture days (CWD) showed a downward trend over the coastal area of China and its sub-regions, there was a generally insignificant upward and downward tendency of other all extreme precipitation indices in the southern and in the northern coastal area, respectively, and an upward trend in the entrie coastal area. Multi-year averages of all extreme precipitation indices except consecutive dry days (CDD) varied largely in the coastal area of China, generally highest in the Huanan coastal area and lowest in the Huabei coastal area, respectively. Primary period of extreme precipitation indices varied from 2- to 7-year in the sub-regions. The abrupt change of extreme precipitation indices occurred mainly in the 1990s and the 1970s in the sub-regions. Extreme precipitation events in the Dongbei and the south of Jianghuai (inclusive) coastal areas tended to be more frequency while in the Huabei and Huanghuai coastal areas were decreasing after mutation. Sub-regions of Huabei, Huanghuai and Jianghuai coastal areas would be suffering from drought but Dongbei, Jiangnan and Huanan coastal areas would be much moist in the future. Except CDD, the other extreme precipitation indices correlated strongly with each other, and exhibited high contributions to the annual total precipitation amount.(3) Impact of extreme climate events on NDVI
The tendency of NDVI in the coastal area of China and its sub-regions showed an upward trend and would be increasing in the coming period. NDVI series in sub-regions got a mutation mainly in the early 21st, followed by the 1990s, and an increasing trend was found after mutation in each sub-region. The vegetation coverage was generally good in the coastal area of China, and the coverage in the south of Jianghuai coastal area (inclusive) was much better than that in the north.
On the interannual scale, the warm extremes and extreme value indices showd a positive correlation with NDVI in the CAC, and DTR showed a negative correlation with NDVI in the north of Huanghuai coastal area (inclusive) but a positive correlation in the south’s. Exreme preciptiaiton events presented a positive correlation with NDVI in the north of Huanghuai coastal area (inclusive). The extreme value indices and DTR both correltated with NDVI strongly on the scale of the year, and NDVI in the Jiangnan coastal area (inclusive) showed a lag effect on the extreme value indices. Extreme preciptiaiton events in the north of Jianghuai coastal area presented a positive correlation with NDVI generally and NDVI in the south of Jianghuai coastal area (inclusive) showed a lag effect on the extreme precipitation events. Extreme high temperature indices and DTR both showed a negative effect on the NDVI in the western of Dongbei coastal area, Huabei and Huanghuai coasta area while a positive effect in the other coastal areas. The current month and the preceding month exhibited a negative and a positive effect on the NDVI in the CAC, respectively. Extreme precipitation indices affected the NDVI in the werstern of Dongbei coastal area, Huabei and Huanghuai coastal areas positively, while in the other coastal areas negatively.
The spatiotemporal variations of extreme climate events and their impacts on NDVI in the coastal area of China were revealed in this paper could privide reference and basis for scientific adaptation, mitigation and response to climate anomalies and coastal zone ecological and environment protection, which were beneficial to the sustainable development of social economy and ecological environment in the coastal area of China.